In the semiconductor industry, fuse elements are widely used in integrated circuits for a variety of purposes, such as improving manufacturing yield or customizing generic integrated circuits. For example, by replacing defective circuits on a chip with duplicate or redundant circuits on the same chip, manufacturing yields can be significantly increased. A fuse disconnected by a laser beam is referred to as a laser fuse, while a fuse disconnected by passing an electrical current, or blowing, is referred to as an electrical fuse, or e-Fuse. By selectively blowing fuses within an integrated circuit, which has multiple potential uses, a generic integrated circuit design may be economically manufactured and adapted to a variety of customer uses.
Typically, fuses are incorporated in the design of the integrated circuits, wherein the fuses are selectively blown, for example, by passing an electrical current of a sufficient magnitude to cause electro-migration or melting, thereby creating a more resistive path or an open circuit. Alternatively, a current that is weaker than the current required to entirely blow a fuse can be applied to the fuse in order to degrade the fuse, thus increasing a resistance through the fuse. The process of selectively blowing or degrading fuses is often referred to as “programming.”
FIG. 1 illustrates a perspective view of a commonly formed electrical fuse, which includes metal line 2, also referred to as fuse element 2, connected to contact pads 4. Contact pads 4 have a significantly greater width than fuse element 2. Fuse element 2 and contact pads 4 are formed in one of the metallization layers. Each of the contact pads 4 may be connected to metal lines in overlying metallization layers through a plurality of vias (not shown). The total cross-sectional area of the vias and the cross-sectional area of contact pads 4 are substantially greater than the cross-sectional area of fuse element 2. Therefore, when a blowing current is conducted, fuse element 2 has a greater current density than the vias and contact pads 4, and thus is blown.
In order to reliably blow the fuse, fuse element 2 preferably has a small cross-sectional area, so that the respective current density, hence Joule effect, is high. The cross-sectional area of fuse element 2 can be reduced by reducing width W and/or thickness T. Currently, the width W of e-Fuses has been reduced to about 0.1 μm or less, and thus there is little room, if any, for further improvement. On the other hand, since fuse element 2 and contact pads 4 are formed in one of the metallization layers, the thickness T equals the thickness of the respective metallization layer. Thickness T, therefore, cannot be customized to satisfy the requirement of e-Fuses. This limits the reduction of the blowing current. A novel fuse structure and methods for forming the same are thus needed.